1. Field of the Invention
The present invention relates to a recording apparatus and, more particularly, to a recording apparatus for recording a digital picture signal having a relatively large number of data bits onto a magnetic tape that can be contained in a relatively small cassette housing.
2. Description of the Prior Art
A D1 format component type digital VTR and a D2 format composite type digital VTR have been developed for use by broadcasting stations in digitizing color video signals and recording the digitized signals on a recording medium, such as a magnetic tape.
In the D1 format digital VTR, a luminance signal and first and second color difference signals are A/D converted with sampling frequencies of 13.5 MHz and 6.75 MHz, respectively. Thereafter, the signals are suitably processed and then recorded on a tape. Since the ratio of sampling frequencies of the signal components is 4:2:2, this system is usually referred to as the 4:2:2 system.
On the other hand, in the D2 format video digital VTR, a composite video signal is sampled with a signal having a frequency 4 times higher than the frequency fsc of a color subcarrier signal and then A/D converted. Thereafter, the resultant signal is suitably processed and then recorded on a magnetic tape.
Since these known D1 and D2 format digital VTRs are designed for professional use, for example, in broadcasting stations, the attainment of high picture quality is given top priority in the design and construction of such VTRs, and the weight and size of the apparatus are not overly important.
In these known digital VTRs, the digital color video signal, which results from each sample being A/D converted into, for example, 8 bits, is recorded without being substantially compressed. As an example, when the known D1 format digital VTR A/D converts each sample into 8 bits with the frequencies noted above, the data rate representing the color video signal is approximately 216 Mbps (megabits per second). When the data in the horizontal and vertical blanking intervals are removed, the number of effective picture elements of the luminance signal per horizontal interval and the number of effective picture elements of each color difference signal per horizontal interval become 720 and 360, respectively. Since the number of effective scanning lines for each field in the NTSC system (525/60) is 250, the data bit rate Dv can be expressed as follows:
Dv=(720+360+360)xc3x978xc3x97250xc3x9760=172.8 Mbps
Even in the PAL system (625/50), since the number of effective scanning lines for each field is 300 and the number of fields per second is 50, it is obvious that the data bit rate in the PAL system is the same as that in the NTSC system. If the redundant components necessary for error correction and the format with respect to such data are considered the total bit rate of picture data becomes approximately 205.8 Mbps.
Further, the amount of audio data Da is approximately 12.8 Mbps, while the amount of additional data Do, such as, data of a gap, a preamble, and a postamble used in editing, is approximately 6.6 Mbps. Thus, the bit rate of information data to be recorded can be expressed by the following equation:
Dt=Dv+Da+Do
Dt=172.8+12.8+6.6=192.2 Mbps.
In order to record such amount of information data, the known D1 format digital VTR employs a segment system having a track pattern comprised of 10 tracks for each field in the NTSC system, or comprised of 12 tracks for each field in the PAL system.
A recording tape with a width of 19 mm is used. There are two types of recording tapes having thicknesses of 13 xcexcm and 16 xcexcm, respectively. To house these tapes, there are three types of cassettes, which are respectively characterized as being of the large type, middle type, and small type. The information data is recorded on such tapes in the above mentioned format with the tape area for each bit of data being approximately 20.4 xcexcm2/bit, which corresponds to a recording density of 1/20.4 bit/xcexcm2. When the recording density is increased, an error tends to take place in the playback output data due to interference between codes or non-linearity of the electromagnetic conversion system of the head and tape. Heretofore, even if error correction encoding has been performed, the above given value of the recording density has been the limit therefor.
By putting all the above described parameters together, the playback times for the cassettes of various sizes and the two tape thicknesses, when employed in the digital VTR in the D1 format can be tabulated as follows:
Although the described D1 format digital VTR can provide satisfactorily,high picture quality for use in broadcasting stations, even if a large cassette housing a tape with a thickness of 13 xcexcm is used, the playback time is at most 1.5 hours. Thus, such a VTR is not adequate for consumer or home use in which a playback time at least sufficient for the recording of a telecast movie is required. On the other hand, in VTRs intended for consumer or home use, the xcex2 system, the VHS system, the 8-mm system, and so forth have been employed. However, in each of these systems for consumer or home use, analog signals have been recorded and reproduced. Although the picture quality of these analog VTRs has been improved to the point where the quality is satisfactory when a video signal is simply recorded and then reproduced for viewing, the picture quality is significantly degraded when the recorded signal is dubbed and copied. Thus, when the recorded signal is dubbed several times, the picture quality will become unacceptable to the viewers.
As is to be appreciated, if the data to be recorded and reproduced are in digital form as, for example, in the case of the above-described D1 and D2 digital VTR""s, signals having acceptable picture quality can be produced even if the signal data are dubbed several times. Thus, while the D1 and D2 digital VTR""s can produce signals of acceptable picture quality even if the signals are dubbed several times, such digital VTR""s are relatively large in size, relatively expensive and, as previously mentioned, are limited to a relatively short record or playback time. As a result, the D1 and D2 digital VTR""s are typically unacceptable for home use.
Thus, the prior art has failed to provide a relatively low-cost VTR for home use which records and reproduces a digital picture signal so as to produce signals having acceptable picture quality when subjected to the above described situations, is of a relatively small size and is capable of recording a reasonably large amount of data.
Accordingly, it is an object of the present invention to provide an apparatus for recording and reproducing a digital picture signal which avoids the above-mentioned disadvantages of the prior art.
More specifically, it is an object of the present invention to provide an apparatus for recording and reproducing a digital picture signal which is capable of recording a relatively large amount of digital picture signal data and is relatively small in size.
It is another object of the present invention to provide an apparatus for recording and reproducing a digital picture signal as aforesaid having a magnetic tape wound in a tape cassette, in which the magnetic tape has a width of no more than approximately 8 mm and a thickness of no more than approximately 7 xcexcm.
It is yet another object of the present invention to provide an apparatus for recording and reproducing a digital picture signal as aforesaid which reduces the number of data bits of the received digital picture signal and records the reduced number of data bits in successive skewed tracks, and in which each track has a width of approximately 5.0 xcexcm, with a recording density of at least approximately 0.8 bits/xcexcm2.
It is still another object of the present invention to provide an apparatus for recording and reproducing a digital picture signal as aforesaid in which each recording head is positioned so as to have an azimuth angle of approximately 20xc2x0.
It is still a further object of the present invention to provide an apparatus for recording and reproducing a digital picture signal as aforesaid in which the magnetic tape is wound on the peripheral surface of a rotation drum so as to have a winding angle of less than 180xc2x0.
According to an aspect of the present invention, an apparatus for recording an input digital picture signal comprises a magnetic tape wound in a cassette and having a width of no more than approximately 8 mm and a thickness of no more than approximately 7 xcexcm; a data processing device for reducing the data of the input digital picture signal by a ratio of approximately 1:9 so as to provide a recordable signal having a reduced data bit rate; and a device for recording the reduced data bit rate signal in successive skewed tracks on the tape with an areal recording density of at least approximately 0.8 bits/xcexcm2 